Waveguides of near-eye displays convey image information toward viewers' eyes from positions outside the viewers' fields of view. The image information conveyed by many such waveguides has an angularly encoded form for projecting virtual images into the viewers' eyes. The near-eye displays present the image information to the viewers within viewing pupils (also referred to as “eyeboxes”), which when aligned with the pupils of the viewers' eyes produce virtual images within the viewer's fields of view.
The image information originates outside the viewers' fields of view in positions such as along the temples of eyeglass frames. Electronic video display data is converted into the image information by optical pattern generators, such as spatial light modulators, combined with focusing optics that angularly transform the spatial patterns or by scanning optics that directly generate angular transforms of spatial patterns.
The waveguides, which can be mounted within the frame fronts of eyeglass frames in place of or in addition to eyeglass lenses, convey the image information from outside the viewers' fields of view into the viewers' fields of view in a form that minimizes the thicknesses of the near-eye displays in front of the viewers' eyes. The waveguides, at least as a goal, occupy limited volumes of space corresponding to the space within which eyeglass lenses are normally held within the eyeglass frames. That is, the waveguides are preferably limited in thickness (i.e., depth) for more closely resembling the dimensions of conventional eyewear.
The waveguides, which generally take the form of transmissive plane-parallel plates, incorporate or are otherwise associated with both input couplings for directing light into the waveguides and output couplings for directing light out of the waveguides in a direction generally along the viewers' lines of sight. Generally, light representing individual pixels within the intended virtual images enters the waveguides through the input couplings in a substantially collimated form distinguished from other pixels within the intended virtual images by vertical and horizontal angles of origin (i.e., the angles through which the chief rays enter the aperture). In many of these waveguides, the collimated beam components (i.e., beamlets) that contribute to the vertical dimension of the virtual images propagate substantially without interruption and converge toward the viewing pupils. However, the collimated beam components (i.e., beamlets) that contribute to the horizontal dimension of the virtual images typically propagate through internal reflections between anterior and posterior surfaces of the waveguides, generally preserving the collimated form of the propagating beam components (beamlets). The output couplings redirect the propagating beamlets out of the waveguides and into the viewers' lines of sight forming the viewing pupils.
The waveguides generally support the propagation of the beamlets for forming the horizontal dimension of the virtual images by total internal reflection. As such, the waveguides can remain substantially transparent to provide unobstructed views of the ambient environment. However, the incidence angles supporting the internal reflections are limited to angles above the so-called “critical angle”, which is the minimum incidence angle at which total internal reflection is supported.
The input and output couplings direct the collimated beamlets into and out of the waveguides over a range of angles corresponding to the angular field of view. For example, the two ends of the waveguides can be fashioned as at least partially reflective prismatic facets that are inclined to the direction of light propagation along the waveguides for reflecting collimated beamlets over a range of angles into and out of the displays.
However, the reflective facets, which must be oversized to fill limited size eyeboxes, tend to direct significant portions of the light beyond the eyeboxes. Beamlets exiting the waveguides at field angles associated with one side of the intended image extend into areas at one side of the eyebox, and beamlets exiting the waveguides at field angles associated with the other side of the intended image extend into areas at the other side of the eyebox. That is, although the waveguides limit the spatial separation between collimated beamlets reflecting within the waveguides at different angles of incidence, the beamlets spatially separate after reflection from exit prism facet through an eye relief distance to the eyebox. Unless optical power is also used, which complicates other matters including vision through the waveguide and chromatic correction, the horizontal dimension of the optical pupil degrades over the distance from the reflective facets to the eyebox.
Diffractive or holographic input and output couplings have also been used to couple light into and out of near-eye display waveguides. However, the diffractive or holographic couplings tend to be chromatically sensitive and special compensations are required to compensate.
Waveguides for near-eye displays have been formed in multiple layers for purposes of homogenization. The interface between layers functions as a beamsplitter or partial reflector for splitting incident beams into two separate beams on each encounter. One portion of the incident beam is reflected within the same layer and another portion of the incident beam is transmitted into another layer. The effect is to widen the initial beam manifest as a lateral displacement of beam portions propagating along the waveguide. Departures from parallelism between the layers can produce cumulative errors in the propagation of beam image components.
Multiple waveguides have been used to convey different color components of virtual images. Each of the waveguides includes different pairing of diffractive optics for injecting the different color components into the waveguides and ejecting the different color components from the waveguides for assembling a color image. Each of the pairings of diffractive optics can be optimized for a different color to reduce chromatic aberrations associated with the use of color sensitive injection and ejection optics. However, each waveguide must be arranged to convey the color components across the entire image so the additional waveguides add to the thickness of the display by a multiple equal to the number of additional waveguides.